The Organic Light Emitting Display (OLED) device possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED display element generally comprises a substrate, an anode located on the substrate, a Hole Injection Layer located on the anode, a Hole Transporting Layer located on the Hole Injection Layer, an emitting layer located on the Hole Transporting Layer, an Electron Transport Layer located on the emitting layer, an Electron Injection Layer located on the Electron Transport Layer and a Cathode located on the Electron Injection Layer. The principle of the OLED element is that the illumination generates due to the carrier injection and recombination under the electric field driving of the semiconductor material and the organic semiconductor illuminating material. Specifically, the Indium Tin Oxide (ITO) electrode and the metal electrode are respectively employed as the anode and the cathode of the Display. Under certain voltage driving, the Electron and the Hole are respectively injected into the Electron and Hole Transporting Layers from the cathode and the anode. The Electron and the Hole respectively migrate from the Electron and Hole Transporting Layers to the Emitting layer and bump into each other in the Emitting layer to form an exciton to excite the emitting molecule. The latter can illuminate after the radiative relaxation.
The OLED can be categorized into two major types according to the driving ways, which are the Passive Matrix OLED (PMOLED) and the Active Matrix OLED (AMOLED), i.e. two types of the direct addressing and the Thin Film Transistor matrix addressing. The AMOLED comprises pixels arranged in array and belongs to active display type, which has high lighting efficiency and is generally utilized for the large scale display devices of high resolution.
The AMOLED display device generally comprises an OLED back plate and an organic material layer located on the OLED back plate. FIG. 1 is a structure diagram of an OLED back plate according to prior art. As shown in FIG. 1, the OLED back plate comprises a substrate 100, a buffer layer 200, a semiconductor layer 300, a gate insulation layer 400, a gate material layer 500, an interlayer dielectric layer 600, a source-drain material layer 800, a pixel definition layer 910 and a support layer 920, which are stacked up from bottom to top, wherein the source-drain material layer 800 comprises a first source 810 and a first drain 820 applied in a switch TFT T100, and a second source 830 and a second drain 840 applied in a drive TFT T200, and the second source 830 serves as an anode of the OLED at the same time, and the pixel definition layer 910 being arranged with an opening 915 correspondingly above the second source 830, and the opening 915 defining an OLED light emitting area on the second source 830, and the OLED light emitting area is employed to form an OLED light emitting layer.
In the aforesaid OLED back plate, the second source 830 is directly formed on the interlayer dielectric layer 600 with a poor surface flatness, and therefore, the surface flatness of the second source 830 is worse. However, the OLED light emitting area usually selects the area with a high surface flatness, and only a relatively flat portion of the surface of the second source electrode 830 can be selected to form the OLED light emitting area. Accordingly, the area of the obtained OLED light emitting area is smaller and the aperture ratio is lower.